Genetic evidence from neurodegenerative diseases suggests disruption in neuronal membrane and protein trafficking pathways is a major contributor to the development of disease however, the underlying biological mechanisms remain poorly understood.1 Synaptic vesicle (SV) trafficking and autophagy are two important pathways governing neuronal function that are often implicated in the development of neurodegenerative diseases.2 Although previously considered independent, many studies have now identified additional roles of SV proteins in autophagy.3-7 For example, many Rab GTPases, major regulators of membrane trafficking, have putative roles in both SV trafficking and autophagy.15-18 A recent study has identified multiple Rab GTPases as substrates of LRRK2,12 a kinase that when hyperactive can cause the most common genetic form of PD.8-12 This suggest a mechanism whereby chronic phosphorylation may lead to dysfunction in membrane trafficking pathways and underlie PD development. In this proposal, I aim to investigate how chronic phosphorylation of Rab GTPases by LRRK2 may contribute to defects in SV cycling and autophagy found in PD. Specifically, this proposal will investigate the role of Rab10 by examining the dependence of its function in these pathways on activation state (Aim 1) and phosphorylation state (Aim2). This will be achieved using biochemical, confocal microscopy, and live imaging approaches in primary neurons from wild type and mutant mice and also through an in vivo mouse model. I hypothesize that phosphorylation by LRRK2 acts as a switch in modulating the use of Rab10 in SV cycling versus autophagy, and predict that chronic phosphorylation results in the dysfunction of these pathways as documented in PD. In Aim3, I will explore a new model system for studying human neurological diseases by generating induced neurons from patient fibroblasts. The use of this model system will not only provide a human system to study PD, but will also allow for a comparison of neuronal membrane trafficking alterations in genetic versus idiopathic PD by examining samples from both populations. Ultimately, the knowledge gained through the proposed experiments will broaden the understanding of Rab GTPases in PD and may foster the development of more targeted approaches for treating PD.